A metal-air battery may include a metal negative electrode and an air positive electrode. Oxygen, which is a strong oxidizing agent, light in weight, and normally available everywhere, is the active material of the air electrode. Since the oxygen is supplied from outside the battery, the interior of the battery can be primarily used to accommodate the negative electrode material. This may give metal-air batteries a large energy capacity.
The requirements for a negative electrode material may include a negative redox potential or strong reducing power, a low molecular weight, and a large valence change during discharge. Candidates include lithium, aluminum, cadmium, cobalt, magnesium, zinc and iron.